Display board assembly
BACKGROUND AND SUMMARY OF THE INVENTION 
     The present invention relates to display boards and, more particularly, to a built-up type display board for showing a house number, name of householder or other symbols. 
     Regular doorplates, signboards, or other display boards are generally made according to order. This is indeed expensive and requires a certain period of time to order a doorplate, signboard or the like. Further, regular doorplates are not clearly visible in the night or dark weather. Therefore, an additional lighting device is necessary. 
     One object of the present invention is to provide a display board assembly which can be made through mass production for reducing its cost. 
     Another object of the present invention is to provide a display board which can be flexibly assembled according to requirement. 
     Still another object of the present invention is to provide a display board which utilizes a photosensor to control its light emitting elements to produce light when it is dark. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a fragmentary perspective view of a symbol display unit according to the present invention. 
     FIG. 2 is a schematic drawing illustrating the connection of one symbol display unit with another. 
     FIG. 3 is a schematic drawing illustrating an operation to couple three symbol display units with a start unit and an end unit. 
     FIG. 4 illustrates a automatic dark turn on power module according to the present invention. 
     FIG. 5 illustrates a light emitting diode (hereafter LED) display module according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to FIG. 1, a symbol display unit in accordance with the present invention includes a front panel 1 attached to a bottom block with a printed circuit board 3 received therein, in which the front panel 1 has a symbol therein, which symbol can be a number, character or sign. 
     A front pale 1 of a symbol display unit in accordance with the present invention comprises a transparent symbol portion 11 and an opaque non-symbol portion 12 on its front face, wherein the transparent symbol portion 11 is tinted colorless, and the opaque non-symbol portion 12 is colored in such a way to present a striking contrast to the transparent symbol portion 11 so that the symbol thereon can be prominent and clearly seen in the day. A bottom block 2 of a symbol display unit according to the present invention has an edge about its periphery extending from the bottom block to the front panel defining a top edge, a bottom edge and two side edges an unitary upper L-shaped projecting end 21 and a lower L-shaped projecting end 22 extending from one side two L-shaped recesses 23, 29 arranged within an opposite side matching the L-shaped projecting ends 21, 22, four stub tenons 24, 25, 26, 27 internally upstanding therefrom in the four corners thereof for the positioning therein of a printed circuit board 3. A printed circuit board 3 of a symbol display unit of the present invention comprises a plurality of light emitting diodes 31 respectively arranged at an area corresponding to the symbol portion 11 of the front panel 1 of such a symbol display unit, a power plug 32 thereon, and a power socket 33 opposite to its power plug 32. Further, the front panel 1 of a symbol display unit comprises and edge about is periphery with two notches 13 corresponding to the power plug 32 and the power socket 33 of a printed circuit board 3. Therefore, when a printed circuit board 3 is received in a bottom block 2 and a front panel 1, the power plug 32 and the power socket 33 of such a printed circuit board 3 are exposed for connection. 
     As illustrated in FIG. 2, two or more symbol display units of the present invention can be conveniently connected together by means of screws 4 or lock pins to form a board assembly. The two L-shaped projecting ends 21, 22 of the bottom block 2 of one symbol display unit are respectively set in the two L-shaped recesses 23, 29 of another symbol display unit and firmly fixed up together by means of screws 4 through the holes thereon. 
     Referring to FIG. 3, a start unit 5 of the present invention comprises two L-shaped recesses 23&#39;, 29&#39; and a power socket 33&#39; corresponding to the two L-shaped projecting ends 21, 22 and the power plug 32 of a symbol display unit for connection (Please refer to FIG. 2). An end unit 6 of the present invention comprises two L-shaped projecting ends and a power plug corresponding to the two L-shaped recesses and the power socket of a symbol display unit connection. In a display board assembly, the start unit 5 and the end unit 6 are respectively structured to compensate for each other and can be secured to a wall be screws 52, 53, 62, 63. Each end unit 6 also comprises a window 61 through which a photosensor therein can detect the intensity of outside light, and a power supply device 7 to convert regular alternating current power to a lower voltage of alternating current power for the operation of the present invention. 
     FIG. 4 illustrates an automatic dark turn on power module according to the present invention. Alternating current power is treated through a power supply device 7 for voltage dropping and rectified by a diode D1 to provide a direct current power. The direct current power thus obtained is sent through a silicon controlled retifier Q1 to a LED module. During the day under good vision condition, photosensor Q2 receives a large amount of light and thus cuts off the circuit to turn off the silicon controlled retifier Q1. According, no direct current power is sent to the LED module. On the contrary, the photosensor Q2 detects less amount of light under a dark condition, and the impedance of the photosensor Q2 increases. After shunt through resistor R1, the voltage from the photosensor Q2 turns on the silicon controlled retifier Q1 to provide the LED module with necessary working voltage. 
     Referring to the LED display module of FIG. 5, a plurality of LEDs are connected into several branches which are disposed in parallel with each other in which each branch is comprised of a current limiting resistor (R2, R3, R4, etc.) connected with several LEDs in series. The impedance of each current limiting resistor is determined according to the total quantity of LEDs in each branch. As described, the present invention utilizes low voltage for its operation. It helps to reduce power consumption and extend LED&#39;s service life.